The invention relates to a continuous process of using pieces of polyurethane foam to form webs of thermoset polyurethane. The invention involves manufacturing useful products such as carpet or flooring underlay, sound-deadening panels, packaging, and cushioning applications, from scrap materials.
Continuous and batch, or discontinuous, processes have been considered for salvaging virgin scrap and scrap recycle polymer. Generally, the processes have been rejected as commercially non-feasible, since most are time consuming, economically inefficient, and environmentally hazardous. For example, batch processes rely on molds, which are cumbersome, involve long cycle times; and produce single product sheets. Moreover, large metal molds or platens conduct heat in an inefficient manner, as in Diessel et al., U.S. Pat. No. 5,185,380. Conventional batch processes often rely on addition of binding agents to the scrap. Depending on the identity, the binding agents can present environmental hazards and can complicate processing. Prior continuous processes for salvaging scrap have some of the same disadvantages as batch processes.
A previous continuous process for compressing virgin polyurethane foam is described in Pettingell, U.S. Patent Re. 32,032 which used hot air suction and temperatures designed to preserve the integrity of the foam""s cell structure. The circulating air would make the use of foam chips impractical (due to flying chips) and the use of temperatures above 365 degrees .F for more than 1 minute is said to char the foam. Col. 5, lines 52-54.
Efforts to heat and compress rigid, thermoplastic scrap foam by continuous process are described in U.S. Pat. No. 3,746,610. In the examples of the ""610 patent, polyhydrocarbon (not polyurethane) foam flakes are heated only to tack temperature, compressed and then cooled to form a composite thermoplastic material. There remains a need for a process suitable for the use of incoming thermoset material and a resulting flexible, high density sheet (not a rigid, low density board), which are objectives that cannot be met by a melting and fusing process. Recycling thermoset scrap foam by batch processes is described in White and Durocher, xe2x80x9cRecycling of Rigid Polyurethane Articles and Reformulation into a Variety of Polyurethane Applications,xe2x80x9d Journal of Cellular Plastics Volume 33, Sept./Oct 1997. The article refers to a glycolysis process, where glycol is added to rigid, thermoset scrap that has been heated sufficiently to break some urethane linkages to form a liquid that includes replacement polyol from glycol. This process produces recyclate polyols that can be mixed with virgin polyols to make rigid foams. The article notes the economic impracticality of glycolysis for flexible foam scrap and the established carpet underlay market for such scrap.
The invention relates to a continuous process for utilizing ground polyurethane foam and to products produced thereby. The result of the process is a continuous foam web or batting. The continuous process comprises providing chips of thermoset polyurethane to form a bed of chips on a continuously moving conveyor, subjecting the bed to heat; subjecting the bed to compression or pressure; and forming a continuous web of product having higher density than the bulk density of the chips.
Utilizing a continuous process that does not require additional chemicals that add cost and could pose environmental hazards, the invention provides increased speed and efficiency in the manufacture of compressed foam sheets of medium-to-high density from recycled thermoset a polyurethane foams such as polyester, polyether and blended foams. The properties of the resulting material (e.g. density, hardness, tensile strength) can be varied and the material may be laminated or fabricated, depending on customers"" needs, and immediately rolled for storage and handling. According to the invention, chemical rebonding between chips of feed material occurs under easily controlled conditions of pressure and temperature not met in any of the prior art disclosures, and provides a more uniform integral product than prior composites.
The invention can be carried out in normal air, without special gases, and preferably employs conductive heating rather than forced air heating. Conductive heating is particularly advantageous with denser foams and thicker sheets.
According to the invention, temporary thermal depolymerization takes place before the material reforms into a coherent web. The process is characterized by conditions of temperature and pressure are effective to cause some isocyanate group regeneration by partial reversal of the polymer forming reactions. It is noted that, during heating, polyol regeneration may also result from polyurethanes produced from polyols. The invention relies on the heat and compression to effect that regeneration of polyol (polyether or polyester) and/or isocyanate groups, via partial reversal of the polymer forming reactions, rather than the independent addition of reagents to the dry chips of thermoset polyurethane. That regeneration results, in turn, in a chemical bonding reaction between the regenerated isocyanate groups and the heated thermoset polyurethane.
The invention does not require addition of binders, adhesives or reagents to the bed of chips; moreover, it does not require lubricants or mold release agents. Accordingly, the continuous web production can be viewed as xe2x80x9ccomprisingxe2x80x9d, as xe2x80x9cconsisting essentially ofxe2x80x9d or as xe2x80x9cconsisting ofxe2x80x9d the process herein described.
The products can be used for manufacture of carpet or flooring underlay, sound deadening panels, gaskets and seals, and in packaging and cushioning applications. The web product can be fabricated or laminated with additional laminates. For example, laminate sandwiches can be formed with thinly peeled virgin polyurethane foam or polyethylene coated paper or other material, both of which mask the sometime multi-color appearance of the rebonded scrap foam and provide a smooth surface to the sheet. Modification of the product is contemplated through the addition of other additives that will yield desired properties, including for example carnauba or other waxes in an amount up to 5% by weight for the purpose of improving the moisture resistant properties of a continuous foam sheet.